1. Field of Invention
The present invention relates to a circuit transmission line. More particularly, the present invention relates to a double waveform method for driving signals through a transmission line.
2. Description of Related Art
Distortion of a signal after passing through a transmission line is one of the major engineering problems in data communication. Because each piece of transmission line has some electrical reactance, different degrees of capacitor effect will appear. In other words, intrinsic capacitance and resistance within the transmission line may trigger any passing voltage signals into characteristic capacitor charging/discharging. If the time constant for the resistance-capacitance (RC) coupling is high, transmission delay is longer and ultimately leads to a longer signal-stabilizing period. In many high-speed transmission environments, accurate reproduction and stability of transmitted voltage from one end of a transmission line to the other is important. For example, signal voltages must be transmitted to a flat panel display rapidly, accurately and in a stable condition. Any deviation in the signal voltages may result in serious errors. Furthermore, as size of the flat panel display is increased, deviation in electrical properties of the liquid crystals inside the panel will be higher. Because the distribution and organization of liquid crystals inside the flat panel display also will lead to some deviation in electrical properties as well, erroneous operation will occur more frequently in practice.
FIG. 1 is a diagram showing an equivalent circuit of a conventional transmission line. Assume a step voltage signal as shown in FIG. 1 needs to be transmitted across a transmission line. When a voltage signal is fed into point A in FIG. 1, the signal will pass by a capacitor 102 and resistor 112 pair, a second capacitor 104 and resistor 114 pair, a third capacitor 106 and resistor 116 pair, a fourth capacitor 108 and resistor 118 pair and so on in sequence before finally arriving at point B. Because the voltage signal has undergone a series of charging/discharging cycles, signal waveform at the output point B is the one shown in FIG. 3. As shown in FIG. 3, an initial voltage Vi input into point A will reach a stable final voltage Vf only after the passage of a period T. Moreover, since B is the most distant point from point A, the amount of voltage distortion will be most intense.